analyzer: fix ICE when handling callback exceeds enode limit [PR97514]

gcc/analyzer/ChangeLog:
	PR analyzer/97514
	* engine.cc (exploded_graph::add_function_entry): Handle failure
	to create an enode, rather than asserting.

gcc/testsuite/ChangeLog:
	PR analyzer/97514
	* gcc.dg/analyzer/pr97514.c: New test.

gcc/analyzer/engine.cc

@@ -1956,8 +1956,9 @@ exploded_graph::add_function_entry (function *fun)
     return NULL;
 
   exploded_node *enode = get_or_create_node (point, state, NULL);
-  /* We should never fail to add such a node.  */
-  gcc_assert (enode);
+  if (!enode)
+    return NULL;
+
   add_edge (m_origin, enode, NULL);
 
   m_functions_with_enodes.add (fun);

gcc/testsuite/gcc.dg/analyzer/pr97514.c

@@ -0,0 +1,18 @@
+/* { dg-additional-options "--param analyzer-max-enodes-per-program-point=0 -Wno-analyzer-too-complex" } */
+
+typedef void (*sighandler_t) (int);
+
+void
+signal (int, sighandler_t);
+
+static void
+kw (int signum)
+{
+  (void) signum;
+}
+
+void
+gk (int ot)
+{
+  signal (ot, kw);
+}